With “In Time,” writer-director Andrew Niccol takes a clever, compelling idea — that time is currency and you can buy your way to immortality or die broke — and beats it into the ground.

For a movie about the importance of maximizing every second, “In Time” ultimately grows repetitive and wears out its welcome. It’s fast-paced and hugely stylish, though, with its great-looking cast and a mix of gleaming, futuristic visuals and grimy, industrial chic.

But Niccol’s high-concept premise raises several nagging questions. Why do all the inhabitants of this dystopian world stop aging at 25, then find themselves with only a year left unless they can buy themselves more? When did this start — what is the purpose? And if Justin Timberlake is so busy working in a factory just so he can afford to live one day to the next, where does he find time to go to the gym?

Yes, among the beautifully photographed images in “In Time” is a shirtless Timberlake, early and often. He stars as Will Salas, who lives in the ghetto neighborhood of Dayton but dreams of moving to the ritzy New Greenwich with his mother (Olivia Wilde in an amusing bit of casting, since she’s three years younger than Timberlake). In one of many inspired details, the amount of time you have glows green as it ticks away on your forearm, and you can share what you have — or take it away — by clasping wrists with another person.

When Will can’t stop his mother’s time from running out — and he’s framed for a crime he didn’t commit — he goes on a revenge spree to steal years from the rich and give them back to the poor. His accomplice: Sylvia Weis (Amanda Seyfried), the beautiful but sheltered daughter of the wealthiest man in town (Vincent Kartheiser), who starts out as his hostage but becomes his enthusiastic partner in crime.

Cillian Murphy is on their tail as a “timekeeper,” a sort of cop who runs around enforcing the rampant theft of hours and minutes in his ever-present, distressed leather coat.

Basically, everyone is gorgeous, high-cheekboned and fashionably dressed in the future. Seyfried’s style would please Anna Wintour with her dark red, blunt-cut bob and tailored, feminine designs. The downside of that, though, is that she has to run in heels — a lot. She and Timberlake are cute and playful together, yet lack the kind of intense chemistry that suggests they’d ever be truly dangerous.

But if you can get past the plot holes and the copious time puns, “In Time” is actually rather brisk, enjoyable entertainment. And with its gaping disparity between the haves and the have-nots causing increasing class tension, it also has the added benefit of being relevant.